Air Down

Air Down Automatically

Okay, you're all at the trailhead and you're getting ready for the back country.   The hubs are being locked, and hissing sounds are in the air as everyone is airing down their tires.  (Some grunting can also be heard from those still trying to remove their quick disconnects.)  Meanwhile, you're relaxing and taking in the view - maybe you're pouring yourself another cup of coffee while everyone else is busy checking the status of their tires.  This is because your tires are automatically airing down, and they will stop right where you want them to stop!  Oasis Off Road makes this neat kit for airing down your tires automatically.  They even work while you are driving.  The kit includes four adjustable deflators, an allen wrench (for setting the deflators), a tire gauge, laminated instructions, and a nice leather pouch to carry it all.

The deflators come in two versions, but the 8-20 pound range is the one you need for the Jeep.  The range is applicable to the desired stopping point.  Once you've set the deflators to your desired pressure setting (you do this in your garage long before you leave for your trip), all that is left to do is remove the valve cap and screw on the deflator. 

Close-up view of one of the Oasis Deflators

But it's a good idea to check them when they're finished deflating just to make sure the setting hasn't changed.  Consistency is the important part.  The kit comes with a low-range pressure gauge that fits in their pouch.  However, while setting each of the deflators, I checked the reading between the three gauges I had in my garage and found the new gauge to read 2 pounds higher than my other two.  So I will be keeping my favorite tire gauge in my center console...

This type of pressure gauge is very handy with its bleeder valve for fine-tuning. 

My favorite tire gauge

The gauge will also hold its reading until you clear the gauge by burping the bleeder valve.

The deflators can be used while you are driving (at slower speeds).   The units are approximately 2" long, but don't stick out too far where they would become vulnerable on a dirt road (you wouldn't want to leave them on in the rocks though).  They come in red, blue, and polished aluminum.  I chose the red so that I'd have a better chance at finding it if I accidentally dropped it (which probably WILL happen).

Deflater - view from the back showing how much it sticks out    Deflater on wheel

Finally, the units are serviceable if they get dirty.  Always using a valve cap will help keep the valve stems clean and clear of debris - helping prolong the efficiency of the deflators.

How low should you go?

The following table can be used as an initial basis for airing down your tires.   Rim width, tire construction, and weight distribution may necessitate the need for adjustments.  The pressures (psi) in this table are applicable for most forms of four-wheeling (up to 20 mph).

Tire Size Gross Vehicle Weight
2000 lbs. 3000 lbs. 4000 lbs. 5000 lbs. 6000 lbs. 7000 lbs. 8000 lbs.
215/75R15 11 13 15 N/R N/R N/R N/R
235/75R15 10 12 14 16 N/R N/R N/R
29x8.5R15 10.5 12.5 14.5 15.5 N/R N/R N/R
30x9.5xR15 9 10 12 14 16 N/R N/R
31x10.5R15 8 9 10 12 14 16 N/R
32x11.5R15 7.5 8.5 9.5 11 13 15 18
33x9.5R15 9 10 12 14 16 N/R N/R
33x12.5R15 7 8 9 10 12 14 16
35x12.5R15 6 7 8 9 10 12 14
36x14.5R15 5 6 7 8 9 10 12
38x15.5R15 4 5 6 7 8 9 10
225/75R16 11 13 15 N/R N/R N/R N/R
245/75R16 10 12 14 16 N/R N/R N/R
265/75R16 9 10 12 14 16 N/R N/R
285/75R16 8 9 10 12 14 16 N/R
295/75R16 7 8 9 10 12 14 16

N/R = Not Recommended